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United States Patent |
5,007,712
|
Kikuchi
,   et al.
|
April 16, 1991
|
Optical pick-up unit
Abstract
In an optical pick-up unit, there is provided with a structure for
supporting a holder holding at least an objective lens through a spring
support assembly so that said holder is movable in both of a focusing
direction and a tracking direction, carried on a carriage capable of
traveling at a high speed in the tracking direction, a spring constant of
the spring support assembly is so set as to be larger in the tracking
direction than in the focusing direction, whereby an amount of a
positioning error of the objective lens produced in the tracking direction
when the carriage is driven at a high speed is reduced. As a result, by
the thus reduced amount of the positioning error of the objective lens,
the optical pick-up unit is improved in access time in comparison with the
conventional optical pick-up unit.
Inventors:
|
Kikuchi; Ikuya (Tokorozawa, JP);
Sato; Ryo (Tokorozawa, JP)
|
Assignee:
|
Pioneer Electronic Corporation (Tokyo, JP)
|
Appl. No.:
|
234547 |
Filed:
|
August 22, 1988 |
Foreign Application Priority Data
| Jan 21, 1988[JP] | 63-6061[U] |
Current U.S. Class: |
359/813; 359/823; 369/44.15 |
Intern'l Class: |
G02B 007/02 |
Field of Search: |
350/255,247,257
369/44,45,46,44.14,44.15
|
References Cited
U.S. Patent Documents
4592037 | May., 1986 | Ohnuki | 350/255.
|
4596444 | Jun., 1986 | Ushida | 350/247.
|
4596448 | Jun., 1986 | Kikuchi | 350/247.
|
4679904 | Jul., 1987 | Kurihara | 350/255.
|
4720088 | Jan., 1988 | Tamura | 350/247.
|
4750164 | Jun., 1988 | Nose | 369/45.
|
4767187 | Aug., 1988 | Gijzen et al. | 350/247.
|
Foreign Patent Documents |
60-197942 | Oct., 1985 | JP | 350/247.
|
Primary Examiner: Arnold; Bruce Y.
Assistant Examiner: Ben; Loha
Attorney, Agent or Firm: Fleit, Jacobson, Cohn, Price, Holman & Stern
Claims
What is claimed is:
1. An optical pick-up unit mounted on a pick-up carriage of an optical disc
player, said pick-up unit comprising:
a holder for holding an objective lens having an optical axis passing
therethrough;
a base mount mounted on said pick-up carriage;
resilient support means for resiliently supporting said holder so that said
holder can be translated in each of a focusing and a tracking direction
relative to said base mount, said focusing direction being parallel to the
optical axis of said lens and said tracking direction being transverse to
said focusing direction; and
wherein said resilient support means comprises first and second pairs of
resilient filamentary members interconnecting between said base mount and
said holder, said filamentary members each being of equal length and
attached to said holder at points equidistant from said optical axis of
said lens, said points lying in a plane which passes through the optical
axis of said lens, said first pair of filamentary members being disposed
in a first plane perpendicular to the focusing direction, and said second
pair of filamentary members being disposed in a second plane spaced from
and parallel to said first plane and perpendicular to the focusing
direction, the filamentary members within each of said first and second
pairs being spaced apart from one another on said base mount and said
holder, and wherein, a greater distance separates the filamentary members
with respect to each of said first and second pairs on the base mount than
on the holder.
2. An optical pick-up unit mounted on a pick-up carriage of an optical disc
player, said pick-up unit comprising:
a holder for holding an objective lens having an optical axis passing
therethrough, said holder having first and second extension members on
direct oppostie sides of said optical axis from each other which extend
along a length of said holder, said first and second extension members
lying in a common plane entirely containing said optical axis;
a base mount mounted on said pick-up carriage and comprising a first wall
being parallel to said common plane passing through said optical axis of
said lens and each of said first and second extension members of said
holder, and a second wall connected and transverse to said first wall;
resilient support means for resiliently supporting said holder so that said
holder can be translated in each of a focusing direction and a tracking
direction relative to said base mount, said focusing direction being
parallel to said optical axis and said trackintg direction being
transverse to said focusing direction;
said resilient support means comprising first, second, third and fourth
resilient filamentary members interconnecting between the first wall of
said base mount and said holder, the first and second filamentary members
being attached to said holder at said first and second extension members,
respectively, and lying in a first common plane, the third and fourth
filamentary members being attached to said holder at said first and second
extension members, respectively, and lying in a second common plane which
is parallel to and spaced from said first common plane, the first and
second filamentary members being attached to the first wall of said base
mount and separated from each other by a distance which is greater than
that which separates said first and second filamentary members on said
holder, and the third and fourth filamentary members being attached to the
first wall of said base mount and separated from each other by a distance
which is greater than that which separates said third and fourth
filamentary members on said holder.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical pick-up unit, and more
particularly to one provided with a holder holding an objective lens etc.
supported by spring members, the object lens being movable in both of a
focusing direction and a tracking direction.
2. Description of the Prior Art
An optical pick-up unit of an information recording/reading apparatus for
recording or reading information from a disc-shaped recording medium
(hereinafter referred to as the disc) is carried on a carriage which is
rectilinearly movable in a radial direction of the disc. In general, a
rotary motor is used as a prime mover for the carriage. A torque of the
rotary motor is transmitted to the carriage through a suitable
gear-reducer mechanism, for example such as one constructed of a rack and
a pinion.
In the information recording-reading apparatus, since the rotary motor has
a limitation in its responsibility, the apparatus has a limitation in its
quick-access ability for driving the optical pick-up unit at a high speed
to position the unit on a desired recording track of the disc.
Consequently, there is a strong demand for a quick-access information
recording/reading apparatus having an optical pick-up unit. In recent
years, in order to realize such quick-access information recording/reading
apparatus, there is employed a linear motor as a means for driving the
optical pick-up unit of the apparatus, the linear motor being excellent in
responsiveness.
As shown in FIG. 1, in the optical pick-up unit, a holder 1 holding therein
an objective lens (not shown) is supported by a conventional
biaxial-support structure constructed of a base mount 3 and four pieces of
wire-like spring members 2a, 2b, 2c and 2d which are parallel to one
another. The biaxial-suport structure supports the holder 1 through the
spring members 2a, 2b, 2c and 2d so as to be movable in two perpendicular
directions, i.e., in an optical-axis direction "A" or focusing direction
and in a direction "B" or tracking direction perpendicular to the optical
axis direction "A". The objective lens functions to converge an optical
beam passed through a hole 3a formed in the base mount 3 toward an optical
disc (not shown).
As described above, in the conventional biaxial-support structure suporting
the holder 1 through the four pieces of the spring members 2a, 2b, 2c and
2d parallel to one another, a minimum resonant frequency f0 of the holder
1 in the focusing direction "A" is the same as that of the holder 1 in the
tracking direction "B". However, since a focusing servo-mechanism of the
optical pick-up unit moves into its retracted position in operation, it is
difficult to set the minimum resonant frequency f.sub.o of the holder 1 in
the focusing direction "A" at a high level. Consequently, in the
conventional biaxial-support structure, it is natural to set the minimum
resonant frequency of the holder 1 at a low level or low frequency.
In case that a linear motor is employed as a means for driving the optical
pick-up unit having the biaxial-support structure so as to realize a
quick-access information recording/reading apparatus having the optical
pick-up unit, an external force exerted by the carriage acts on the holder
1 through the wire-like spring members 2a, 2b, 2c and 2d since the
carriage carrying the optical pick-up unit is operated under a condition
that the focusing servo is actuated while the tracking servo is not
actuated. In this case, the minimum resonant frequency f.sub.o of the
holder 1 in the tracking direction is low. This means that an assembly of
the spring members 2a, 2b, 2c and 2d of the optical pick-up unit is low in
its spring constant in the tracking direction. Consequently, the objective
lens in the holder 1 is moved to a position slightly deviated from its
neutral position when the quick-access operation of the optical pick-up
unit is conducted, whereby a positioning error is produced at this time.
Due to the existence of such positioning error or a positioning error
caused in a tracking-error detection system employing a push-pull method
and the like, the conventional optical pick-up unit is poor in convergency
on a desired track of the disc to take much access time therefor.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an optical pick-up unit
having a biaxial-support structure capable of providing quick access.
According to the present invention, there is provided: an optical pick-up
unit comprising an objective lens, a spring means for supporting the
objective lens and a base mount for supporting the objective lens through
the spring members, the improvement wherein: the optical pick-up unit is
carried on a carriage capable of traveling at high speed in a tracking
direction; and the objective lens is supported by the spring means so as
to be swingable in both of a focusing direction and the tracking
direction, a spring constant of the spring means being larger in the
tracking direction than in the focusing direction.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of the conventional optical pick-up unit
having the conventional biaxial-support structure;
FIG. 2 is a perspective view of the optical pick-up unit according to the
present invention, illustrating the biaxial-support structure of the
optical pick-up unit;
FIG. 3(A) is a plan view of the linear motor serving as a means for driving
the optical pick-up unit according to the present invention; and
FIG. 3(B) is a side view of the linear motor shown in FIG. 3(A).
DESCRIPTION OF THE PREFERRED EMBODIMENT
Now, an embodiment of the present invention will be described hereinbelow
in detail with reference to the drawings.
In FIG. 2 in which a biaxial-support structure of an optical pick-up unit
of the present invention is shown, a holder 1 holding therein an objective
lens is supported on a base mount 3 through a four pieces of wire-like
spring members 2a, 2b, 2c and 2d so as to be swingable in both a focusing
direction "A" and a tracking direction "B". Each pair of the spring
members 2a, 2b, 2c and 2d are disposed in each plane perpendicular to the
focusing direction "A". Each of the spring members 2a, 2b, 2c and 2d is
constructed of a spring or a wire prepared through an etching process. In
the embodiment of the present invention shown in FIG. 2, a pair of the
spring members 2a and 2b are disposed in a front mutual plane
perpendicular to the focusing direction "A", while the other pair of the
spring members 2c and 2d are disposed in a rear mutual plane which is
parallel to the front mutual plane and perpendicular to the focusing
direction "A". As is clear from FIG. 2, the spring members 2a and 2b are
more spaced apart from each other at their end portions adjacent the base
mount 3 than at their end portions adjacent the holder 1. In the same way,
the spring members 2c and 2d are more spaced apart from each other at
their end portions adjacent the base mount 3 than at their end portions
adjacent the holder 1. As a result, a spring constant of an assembly of
the spring members 2a, 2b, 2c and 2d is larger in the tracking direction
"B" than in the focusing direction "A". As shown in FIGS. 3(A) and 3(B),
the thus constructed optical pick-up unit 4 having the biaxial-support
structure is carried on a carriage 5.
In the embodiment of the present invention shown in FIGS. 3(A) and 3(B),
the carriage 5 is movably engaged with a guide rail 7 which is supported
at opposite supporting portions 6a and 6b of a base 6. A magnetic circuit
10, which is constructed of a yoke 8 and a magnet 9 and has an elongate
shape forming a magnetic-field area extending along a traveling direction
of the carriage 5, is fixedly mounted on the base 6 through a mounting
plate 11. A movable coil 12 is supported by a coil holder 13 so that at
least one part of the movable coil 12 is positioned in the magnetic-field
area of the magnetic circuit 10 in a side opposite to the optical pick-up
unit 4 with respect to the guide rail 7. A movable-coil type linear motor
14 is constructed of the magnetic circuit 10 and the movable coil 12, and
drives the optical pick-up unit 4 in the tracking direction "B" or radial
direction of the disc through the carriage 5.
In the optical pick-up unit 4 employing the thus constructed linear motor
14, the carriage 5 is good in responsibility so as to be precisely
operated during the tracking operation since the linear motor 14 is
excellent in its responsibility. Consequently, load is supported by the
carriage 5 in a low frequency area of the tracking servo while supported
by the four pieces of wire-like spring members 2a, 2b, 2c and 2d in a high
frequency area thereof. In addition, in the biaxial-support structure of
the optical pick-up unit shown in FIG. 2, a spring constant of an assembly
of the four pieces of wire-like spring members 2a, 2b, 2c and 2d is
larager in the tracking direction "B" than in the focusing direction "A".
Consequently, it is possible to decrease a positioning error of the
objective lens in the holder 1 deviated from a neutral position of the
objective lens 1a even when the carriage 5 is moved at a high speed to
realize quick-access operation of the optical pick-up unit 4, whereby it
is possible to reduce access time for a desired track of the disc in
comparison with the biaxial-support structure employed in the conventional
optical pick-up unit shown in FIG. 1.
As described above, in the optical pick-up unit of the present invention,
since the spring constant of the assembly of the spring members for
supporting the objective lens is larger in the tracking direction than in
the focusing direction, it is possible to reduce the amount of the
positioning error of the objective lens produced in the tracking direction
when the carriage of the optical pick-up unit is driven at a high speed in
quick-access operation. Consequently, by the thus reduced amount of the
positioning error, the optical pick-up unit of the present invention is
superior in access time to the conventional optical pick-up unit.
Furthermore, it is to be understood that the holder 1 may hold not only the
objective lens but also other optical elements such as a beam splitter and
an optical beam source, if preferred.
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